Are All Pluripotent Stem Cells Equal?

Research cloning of humans has always been controversial, because the technology (if ever perfected) would require women’s eggs — many, many eggs if it led to therapies — and would certainly make human reproductive cloning technically more feasible. There were therefore sighs of relief when Shinya Yamanaka discovered how to reprogram readily available somatic cells to become pluripotent, for which he won a Nobel Prize.

Induced pluripotent stem cells (iPSCs) were such an exciting development that many people thought that there was no longer any point in pursuing research cloning, or generating pluripotent embryonic stem cells via nuclear transfer (NT-ESCs). After all, it hadn’t been done after years of trying. But not everyone agreed.

Last year, a team at Oregon State led by Shoukhrat Mitalipov did report success in generating NT-ESCs, and in 2014 two other teams duplicated the result: one led by Dieter Egli’s team at the New York Stem Cell Foundation, the other a collaboration between the Korean Cha Institute and Advanced Cell Technology.

The stakes were raised further when a consortium (including Mitalipov’s team) published a paper in Nature in July that claimed that NT-ESCs were clearly better than iPSCs. Comparing both with stem cells derived from standard IVF embryos, this paper asserted that the iPSCs had flaws, whereas:

human somatic cells can be faithfully reprogrammed to pluripotency by SCNT [somatic cell nuclear transfer] and are therefore ideal for cell replacement therapies.

Not so fast.

A new study led by Dieter Egli’s team (but again including Mitalipov) was just published in Cell, comparing NT-ESCs and iPSCs:

The two cell types showed similar genome-wide gene expression and DNA methylation profiles. … The occurrence of these genetic and epigenetic defects in both NT-ESCs and iPSCs suggests that they are inherent to reprogramming, regardless of derivation approach.

This is particularly noteworthy, coming as it does from people who have been promoting and working on SCNT for many years.

For more detailed analysis, see the Stem Cell Blog of UC Davis professor Paul Knoepfler. He makes the strong point that, given the ethical and practical problems with cloning, NT-ESCs really would have to be significantly better than iPSCs to be worth pursuing — and the new research suggests that they are not.

Nevertheless, all the scientists involved advocate pursuing all lines of research, specifically including nuclear transfer, even though they oppose using it for human reproduction. Which provides further support for the longstanding argument that, at a minimum, the United States needs a firm, specific, national law banning human reproductive cloning.

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